When "The Love Spell Potential" airs on Thursday (May 9), it will prove to be a pivotal episode for
"Big Bang Theory" fans. As the penultimate episode of the show's sixth season, the half-hour finds the whole cast (minus Koothrappali) playing a game of Dungeons & Dragons together, leading to a remarkable shift in Sheldon (
Jim Parsons) and Amy's (
Mayim Bialik) relationship.

2. The girls wind up playing with their guys after a trip to Vegas is aborted when Amy breaks a TSA agent's nose during a pat down at the airport, finding herself placed on the no-fly list. Hoping to alleviate her embarrassment, Penny (
Kaley Cuoco) tells her, "Oh, it's not so bad. You lost money, you're filled with shame, you got groped by a stranger -- I mean, that's Vegas. You nailed it." Perfect.

3. Raj (
Kunal Nayyar) leaves the D&D game early to take Lucy (guest star
Kate Micucci) on what turns out to be quite an awkward date, in which he encourages her to take a chance on things that scare her. It nearly blows up in his face, but there's some wonderful emotional development between the two that's a real victory for the character.

4. Penny uses the D&D game to give her a taste of the Vegas action she's missing out on. After a successful role of the die, she suggests playing for money. Sheldon's perfect reply? "Even better than money, you gained experience points."

5. A turn in the game leads to a very honest discussion between Amy and Sheldon about the intimacy (or lack thereof) in their relationship. It's a surprisingly touching moment buoyed by some fantastic acting from Parsons and Bialik. The evolution of Sheldon since the writer's brought Amy into his life has been such a treat. Tonight's episode is no different.